1. Field of the Invention
The invention relates to downhole tools for subteranean wells, and particularly to a method and apparatus for establishing communication with a downhole portion of a control fluid pipe extending from the well surface to the downhole tool.
2. Summary of the Prior Art
There are many downhole tools which are responsive to fluid pressure transmitted through a small auxiliary line, sometimes referred to as a hydraulic control line. These lines transmit fluid from the top of the well and enter the interior of production tubing, a work string, casing, or the like, at some point at a depth in the well. Safety valves are typical of such hydraulically activated downhole tools.
A very popular form of a downhole safety valve comprises the so-called "full bore opening" type which refers to a safety valve wherein the bore opening through the valve when it is disposed in its open position is substantially equal to the internal bore diameter of the tubing string in which the safety valve is incorporated. Such full bore opening valves may employ a rotatable ball or a pivoted flapper as the shiftable valve head. In either case, the valve head is shifted to its full open position by an actuating sleeve which is axially shiftably mounted within the bore of the valve housing and is operated by one or more hydraulic cylinders to shift the actuating sleeve downwardly and effect the movement of the valve head to its full open position. Pressure control fluid for operating the cylinder is supplied from the surface by the small diameter pipe or tubing which communicates with a control fluid passage in the wall of the valve housing, or through a nipple disposed in the production or work string.
A valve of this general type is shown in U.S. Pat. Nos. 4,503,913 and 4,796,705. The latter patent provides a secondary actuating cylinder for effecting the locking of the movable head of the safety valve in its full open position in the event of any failure or defect in the operation of the primary cylinder.
It is highly desirable to replace any defective safety valve by a functional safety valve, and this has been accomplished in the past by inserting so-called in-tubing safety valve within the bore of the original defective safety valve while the original defective safety valve is in its locked, full open position. Such replacement valves are generally inserted by wireline, hence the problem arises as to how the already installed control fluid piping can be utilized to effect the control of the replacement valve.
U.S. Pat. No. 3,696,868 discloses an in-tubing replacement valve for an installed defective safety valve wherein the wall of the actuating sleeve for the defective valve is perforated prior to the insertion of the replacement valve to provide communication with the existing control fluid conduit. Obviously, the production of perforations in an installed sleeve without damaging surrounding elements is a difficult operation.
Prior art arrangements have also utilized ports in the original valve housing communicating with the control fluid conduit and provided seal elements for such ports or threaded plugs which were then removed by the insertion of the replacement safety valve. Obviously, any time a seal or threaded plug is employed in a downhole environment, there is a distinct possibility that such seal or threads will leak and produce undesirable effects on the operation of the well.
U.S. Pat. No. 3,799,258 proposes the utilization of a hollow, shearable threaded plug traversing the wall of the valve housing with the inwardly projecting end of the plug being sheared off by a sleeve which is moved downwardly by "a suitable tool". This arrangement has several obvious disadvantages. Since the original safety valve may function properly for many years, the successive passages of well treatment and/or other tools downwardly through the safety valve always involves the danger that the inwardly projecting end of the hollow plug may be accidentally sheared off, thus rendering the installed safety valve inoperative. Furthermore, leakage around the threaded plug by high pressure, highly corrosive well fluids is a constant threat.
Accordingly, the prior art has not provided an adequate solution to the problem of effecting trouble free fluid communication of control fluid to a replacement in-tubing safety valve through the control fluid piping already existing in an installed defective safety valve.